It is known that certain oil wells produce crude oils that contain substantial amounts of asphaltenic and/or paraffinic hydrocarbons, which hydrocarbons can form undesirable plugs in the well bore or in the well tubing associated with the oil well. Often, the oil well can become plugged with deposits of acid-soluble material, such as calcium carbonate or clays combined with such asphaltenic and/or paraffinic hydrocarbons.
For a substantial number of years, oil wells have been acidized by an aqueous solution of an acid, such as hydrochloric acid, hydrofluoric acid, acetic acid, and the like, and mixtures thereof. Generally, a mutual solvent for oil and water is used in association with such acid. Of course, the acid can contain, or can be preceded by, or can be followed by such mutual solvent. However, the normally used mutual solvents are not very good at dissolving or stripping asphaltenic hydrocarbons.
Loomis, et al., in U.S. Pat. No. 2,124,530; Dunlap, in U.S. Pat. No. 3,254,718; and Gidley, in U.S. Pat. Nos. 3,481,404 and 3,548,945, provide examples of such mutual solvents. A typical mutual solvent should avoid emulsions, displace the oil, and leave the solid surfaces water-wet. Jones, et al., in U.S. Pat. No. 3,819,520, provide a mixed alcohol solvent that is suitable for acidizing oil and gas wells. This mixed alcohol is a mixture of an octanol and a lower alcohol, which may be ethanol, a propanol, or tertiary butanol. Jones, et al., disclose that such a mixture may be used with, ahead of, or behind aqueous acid solutions that are employed to acidize wells.
There has now been found a solvent system that readily strips or dissolves asphaltenes, permitting the acid to contact and solubilize the acid-soluble portion of the solids formation.